What Cell Found in Bone Functions to Deposit Bony Matrix, Resulting in the Growth of Bone Tissue?

BONE*

B.M. Thomson , in Encyclopedia of Human Nutrition (Second Edition), 1998

Bone Types, Composition and Construction

There are two types of bone in the skeleton – flat bones, e.g., the skull, and long basic, due east.1000., the femur. The principal anatomical features of a long os are shown in Figure 1 .

Effigy 1. The anatomy of a long bone, e.g., the femur. Inset shows an enlarged section of cortical bone.

Bone matrix

Bone matrix is a composite material that derives its forcefulness from a pinch-resistant mineral phase and a tension-resistant network of collagen fibers. Os's mineral stage – calcium hydroxyapatite, Ca _ten(PO₄)_{half dozen}(OH)₂ – is subdivided into a mosaic of tiny microcrystallites, thereby creating a large surface expanse for ion exchange and limiting the spread of cracks. Os matrix also contains a number of specialized noncollagenous proteins, such as osteocalcin, osteonectin and osteopontin.

Macroscopic compages

2 types of internal os architecture are visible to the naked eye. Cortical os, the stronger but heavier of the ii forms, comprises the outer wall of all bones and fulfils a mainly mechanical function (see insert, Figure i ). It consists of parallel cylinders of matrix (osteons) arranged along the load-bearing axis of the bone.

Inside each osteon the matrix is deposited in concentric layers, each ii–iii   μm thick, with a predominant fiber management (like multilayer plywood). The central culvert of each osteon contains bone cells, blood vessels and nerves.

Trabecular bone, the second architectural form, is found at the ends of long bones and in the middle of the vertebrae. Information technology consists of a latticework of bony struts, each 100–500   μm thick. Although weaker than cortical bone, it is more cellular and hence more metabolically active.

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Dedifferentiation and Stalk Cells

Brian K. Hall , in Bones and Cartilage (Second Edition), 2015

Demineralised bone matrix (ordinarily as a powder) from middle-aged humans is a more effective osteoinducer than is pulverization from individuals who are pre- or immediately postal service-puberty. Human rib periosteal cells from younger individuals produce cartilage and os when transplanted in vivo. Cells from older individuals do not (Jergesen et al., 1991; Nakahara et al., 1991). A limitation of bone powder as an agent to evoke osteogenesis from mesenchymal stalk cells is that the powder sequesters calcium and phosphate from the culture medium, depleting its effectiveness (Pflum et al., 2013).

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Maintenance Awry – Chondrodysplasias and Achondroplasia

Brian Thousand. Hall , in Bones and Cartilage (2nd Edition), 2015

Vitamin D

Every bit outlined in Box 1.i, vitamin D plays an of import office in the mineralisation of cartilage and bone. Vitamin D deficiency can result in rickets in children and in osteomalacia in adults. Excess vitamin D (hypervitaminosis-D) and hyperthyroidism in mammals uncouple bone formation from resorption, 2 processes normally tightly correlated, as discussed in Chapter 15.

Implanting demineralised bone matrix into soft tissue or muscle is an effective way to induce ectopic os formation. Demineralised allogeneic bone matrix from vitamin D–scarce rats, implanted into rats with normal vitamin D levels, is a less effective bone inducer than matrix from control animals. Fewer osteoblasts are induced – perchance, it was thought, because the vitamin D–scarce matrix lacks a mitogen present in normal matrix. We know that vitamin D–deficient rat bone has less Tgfß than normal bone and that administering 1,25 vitamin D _three to vitamin D–deficient rats increases Tgfß by 100%. Similarly (or conversely?), demineralised bone matrix from normal rats implanted into vitamin D–deficient rats induces normal amounts of cartilage; less bone is produced than in control rats, however, and the os that forms is abnormally mineralised unless vitamin D is added ^d .

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Osteoblast and Osteocyte Diversity and Osteogenesis In Vitro

Brian K. Hall , in Basic and Cartilage (2d Edition), 2015

Osteonectin

Some 10% of the protein in bone is made up of the 32,000-MW ECM protein osteonectin (or SPARC: secreted protein, acidic, cysteine-rich).

Present in bone matrix with mineralisation, osteonectin links collagen to hydroxyapatite, serves equally a nucleus for mineralisation and regulates the germination and growth of hydroxyapatite crystals. Osteonectin also functions as a secreted rut-daze protein ( Nori et al., 1992). Cataracts and lens anomalies are consequences of osteonectin deficiency in mice.

Patterns of expression of osteonectin mRNA, while similar in rats and mice, are not universal: osteonectin is present in lamprey but not in mammalian livers. Invertebrates are reported to lack osteonectin (Ringuette et al., 1991), although Alison Cole in my laboratory found that an antibiotic against vertebrate osteonectin reacts with the ECM of sabellid polychaete and hemichordate skeletons (Cole and Hall, 2004b).

Within skeletal tissues, osteonectin is expressed in osteoprogenitor cells, osteoblasts, immature (just not old) osteocytes, hypertrophic chondrocytes (HCCs) of mineralising cartilage, fracture callus and ectopic ossification, the latter as seen in fibrodysplasia ossificans progressiva (discussed in Chapter 11). In human and avian embryos calvariae, growth plates, skin and perivascular cells comprise the highest levels of osteonectin mRNA ¹⁰ .

In chicken tibial growth cartilage, osteonectin is expressed in the cells of all zones but only in the ECM in the mineralising zone. Similarly, osteonectin is expressed in the hypertrophic chondrocytes, mineralised matrix and perichondrium of the mandibular condylar cartilages. Chondroid as well contains osteonectin, for which see Chapter 5. Osteonectin mRNA is up-regulated by dexamethasone, retinoic acrid and vitamin D_iii ¹¹ .

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Vitamins: Vitamin Grand☆

K.H. de Borst , ... P.A. Morrissey , in Reference Module in Nutrient Science, 2016

Bone Vitamin K-Dependent Proteins

There are several bone matrix proteins that contain Gla, of which osteocalcin (OC) and matrix Gla protein (MGP) are the most widely studied ( Table ii). OC is an osteoblast-derived, specific vitamin K-dependent protein that besides contains hydroxyproline and is the most arable of all the noncollagenous bone matrix-bound proteins. It has a molecular mass of 5700   Da and contains 3 Gla residues, which give this protein a high affinity for hydroxyapatite, in fact much higher than its analogousness for calcium. The synthesis of OC is nether the regulatory command of the agile vitamin D metabolite, i,25-dihydroxyvitamin D (1,25OHD), and its release into the circulation provides a sensitive index of vitamin D action. While a loftier proportion of newly synthesized OC is incorporated into bone, approximately 30% of it is released into the apportionment and serum levels of the protein are used widely as an indicator of the charge per unit of bone formation. The precise physiological role of OC remains unclear. The less well characterized MGP has a molecular mass of 9600   Da and contains 5 Gla residues and in contrast to OC, which is exclusively associated to mineralized tissues, MGP is nowadays in cartilage and is expressed at a high rate in many soft tissues (heart, kidney, lungs), in addition to os. More recently, another protein very rich in Gla residues was identified and named Gla-rich protein (GRP). This 10.2-kDa secreted protein contains 16 γ-carboxyglutamic acid (Gla) residues in its 74-residue sequence, making it the poly peptide with the highest Gla percent currently known. Similar MGP, GRP is present in cartilage equally well as in bone and soft tissues. In that location is no significant sequence homology between GRP and the Gla-containing region of any currently known vitamin K-dependent poly peptide.

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Cells to Make and Cells to Break

Brian K. Hall , in Basic and Cartilage (Second Edition), 2015

Proximity to Bone Matrix

Osteoclasts depend on the proximity of bone matrix to acquire their characteristic morphology and to express their physiological action. Y'all would recall, therefore, that there would be no incentive to attempt to isolate osteoclasts. Nevertheless, methods for isolating populations of osteoclasts were developed in the early 1970s. Farther development of these procedures to the betoken where osteoclasts can be cultured with os chips, with or without the addition of osteoblastic cells, has revealed how osteoclasts resorb and, possibly every bit chiefly, revealed a coupling between osteoclasts and osteoblasts to issue that resorption ² .

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Bones and Teeth, Histology of

Mary C. Maas , in Encyclopedia of Marine Mammals (2nd Edition), 2009

A Bone Structure and Composition

Bone consists of highly calcified, intercellular bone matrix, and iii types of cells—osteocytes, osteoblasts, and osteoclasts. The outer surface of bone is covered by periosteum, which is bound to os by bundles of collagen fibers known equally Sharpey'due south fibers, and the inner bone surface is lined with endosteum ( Fig. 1). Periosteum is thicker than endosteum, simply both consist of fibrous connective tissue lined with osteoprogenitor cells, from which osteoblasts are derived. Osteoblasts are the cells that synthesize os matrix proteins and are active in bone matrix mineralization. Os matrix (also known as osteoid) consists of virtually 33% organic affair (mostly Type I collagen) and 67% inorganic matter (calcium phosphate, by and large hydroxyapatite crystals). The osteoblasts occur equally simple, epithelial-like layer at the developing bone surface. Every bit the bone matrix mineralizes, some osteoblasts become trapped in pocket-size spaces within the matrix (lacunae). These trapped osteoblasts become osteocytes, the cells responsible for maintenance of the bony matrix. Each lacuna holds simply a single osteocyte just is connected with adjacent lacunae by microscopic canaliculi, which house cytoplasmic processes of the osteocytes. Osteoclasts are big, multi-nucleated cells that occur in shallow erosional depressions (Howship's lacunae) on the resorbing os surface and secrete enzymes that promote local digestion of collagen and dissolution of mineral crystals.

Figure i. (A) Schematic model of the wall of a mammalian long-bone diaphysis, consisting of an outer layer of compact bone and an inner layer of cancellous bone, surrounding a primal medullary crenel. Periosteum covers the outer bone surface, and endosteum covers the inner bone surface. (B) Enlarged diagram of periosteum and compact os in (A). 1, osteon; 2, haversian canal; 3, interstitial lamellae; four, outer circumferential lamellae; 5, cancellous bone; half dozen, Volkman'southward canal; 7, periosteum; viii, Sharpey's fibers; 9, lacuna; x, concentric lamellae. Adapted from Ten Cate (1989).

Bone is usually classified co-ordinate to its gross appearance as cancellous bone (bone with numerous, macroscopic interconnecting cavities, or trabeculae, as well known as spongy or trabecular bone) or compact bone (dense lamellar bone without trabeculae), simply both types have the aforementioned basic histological construction. In a typical mammalian long bone the diaphysis (shaft) is composed predominantly of compact os, with cancellous bone confined to the inner surface effectually a central, medullary crenel (Fig. 1A), while the epiphyses (articular ends) consist more often than not of cancellous bone overlain by a thin, smooth layer of meaty os. In short bones a core of cancellous bone is completely surrounded by meaty bone, and in the flat basic of the skull, inner and outer plates of compact bone are separated by the diploë, a layer of cancellous bone.

Bone also can exist classified histologically, as woven (chief) bone and lamellar (secondary) bone. Woven os, or chief os has an irregular construction and is usually replaced in adults by the more highly mineralized lamellar bone. Lamellar bone is organized into thin layers (lamellae), unremarkably 3–7   μm thick, which incorporate parallel collagen fiber bundles. Lacunae containing osteocytes are located between lamellae. There are three types of lamellae: concentric, interstitial, and circumferential (Fig. 1B). Concentric lamellae are bundled in circular layers around a long axis, the haversian culvert, which is a vascular channel containing blood vessels, nerves, and connective tissue. Adjacent vertical channels are connected by more horizontally oriented vascular channels (Volkmann's canals). The entire complex consisting of several layers of concentric lamellae around a vascular channel is known as an osteon or haversian system. Interstitial lamellae, which appear as irregularly shaped areas between adjacent osteons, consist of lamellae that are remnants of osteons destroyed during os remodeling. Circumferential lamellae are arranged parallel to each other and comprise the outer circumferential lamellae laid down next to the periosteum and the inner circumferential lamellae laid down next to the endosteum.

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Bone

Brian K. Hall , in Bones and Cartilage (Second Edition), 2015

Osteones

The basic structural elements of mineralised cortical bone matrix in mammals and larger tetrapods are known every bit osteones, which come up in different types. Groups of osteones form a Haversian system.

A master osteone (Figure 2.3) has a fundamental culvert that is less than 100   µm in diameter and contains two or more blood vessels. Primary osteones lack a delimiting cement line or interstitial lamellae. A secondary osteone has a larger canal, a single primal blood vessel, is limited externally past a cement line and is wedged between interstitial lamellae. The lamellae may be concentrically bundled as in a Haversian system (Figure 2.2), circumferential as in near-surface bone, or interstitial every bit in remnants of old osteones. The basic of many fish lack osteones or have merely primary osteones. Dense bones (Tabular array two.3) have many secondary osteones (Figure ii.7).

Table ii.3. Some of the Densest Mammalian Bone ^a

Species	Bone	Density (1000/cc)
Mesoplodon densirostris (Blainville's beaked whale)	Mesorostral ossification	2.three–ii.half-dozen
Mesoplodon carlhubbsi (beaked whale)	Mesorostral ossification	2.40
Physeter macrocephalus (sperm whale)	Tympanic bulla	2.sixteen
Trichechus inunguis, T. manatus, T. senegalensis (Amazon, Westward Indies and West African manatees)	Rib	1.81
Caretta caretta (loggerhead turtle)	Humerus	1.33
Delphinus delphis (mutual dolphin)	Rostrum	0.79
Elephas maximus (Asian elephant), Loxodonta africana (African elephant)	Ivory	1.71

a

From information assembled by MacLeod (2002) and Maffucci et al. (2013).

Figure 2.7. Diverse ways of visualising the distribution and orientation of trabeculae, illustrated using the proximal end of the human being femur. (A) The bone is pricked with an awl and stain is rubbed into the surface. Removal of excess stain leaves residual stain in 'splint lines' that reveal fibre bundle and osteone orientation. Method developed by Benninghoff in the mid-1920s. Run across too Figure 31.ane. (B) A diagrammatic representation of pressure (p) and tension (t) trabeculae as depicted by Meyer (*1867), whose research is discussed in Chapter 32. (C) A longitudinal section of dried bone. Compare the trabecular organisation with (B) and with that of a human femur in Figure 31.2.

Modified from P. D. F. Murray (*1936).

Osteone life spans and the fourth dimension it takes to produce an osteone vary from species to species and clade to clade. It takes a 2-yr-old cat (Figure ii.eight) l days to make an osteone; a 45-year-old man needs 100 days. Because the average life span of homo osteones is 15 years, merely 0.05% of our skeletons are turned over per day. The charge per unit of osteone mineralisation is non uniform either; 70% of mineralisation occurs inside one–2 days of deposition of osteoid, and the remaining 30% can take many months. These rate differences go important when assessing pathological states, particularly in metabolic os diseases ²⁶ .

Figure 2.8. A typical true cat, relaxed however alert, takes l days to make an osteone.

Photographed by the author.

Examination of the kinetics of secondary Haversian systems in dogs reveals ix.2 osteoclasts per secondary osteone, nine.1 nuclei per osteoclast, eleven.v days equally the average time nuclei spend in osteoclasts and 7 nuclei per day as the turnover charge per unit. Human cortical os contains 3 types of secondary osteones, which accept like biological lifetimes. Some 90% of the man osteone population comprises unremodelled secondary osteones, with age- and gender-related changes seen in the cortical os of the ribs. Some osteones, given the name 'waltzing osteones', drift through cortical bone matrix as they – the osteones – are remodelled. Frost (1964) defined this as 'a Haversian arrangement in which there is continuous resorption on one side and continuous formation on the other. As a outcome the arrangement becomes flattened in one plane and elongated transversely to this plane, and in effect "waltzes" through the cortex' (p. 151) ²⁷ . Robling and Stout (1999) produced an excellent assay with a superb series of micrographs of the morphology of 'globe-trotting osteones' as basic multicellular units (BMUs) in the cortical os of humans and baboons. More recently, mathematical models accept been developed and combined with double tetracycline labelling to runway the life history of single cortical BMUs (Buenzli et al., 2014).

The standard histology textbook gives the impression that all mammalian os is fine lamellar bone containing numerous secondary osteones. In fact, this picture pertains only to human os, and even and then not to all human os. Surveys of mammalian bone are available, notably those of Enlow and Brown (1958), Enlow (1966a) and I.J. Singh et al. (1974), the latter including a valiant attempt at quantification based on the number and size of primary longitudinal canals and the number of lacunae and empty lacunae.

Variation includes areas of os lacking primary or secondary osteones, acellular or avascular areas and necrotic (expressionless) areas. Moreover, the presence or extent of such regions varies from bone to bone within an private, with age for a given bone, and between individuals. One side of a os may be highly vascularised and the other avascular. Osteones change with historic period of the osteone and of the individual (see department on ageing in subsequent text of this chapter). A highly sophisticated knowledge of the microenvironment in which bone and basic develop is required before we can translate this diversity of expression of the differentiated state of osteocytes. One of the aims of the volume is to marshal and analyse some of that evidence.

Osteones tin be detected in ground sections of fossilised os. A histological assay of tibiae from an early bird was used by Houde (1987) to propose that Hesperornis had osteones similar to those of most living (neognathous) birds. The Upper Permian amphibian (temnospondyl) Australerpeton cosgriffi had abdominal dermal scales of primary os with prominent vascular canals. Osteones were present, but only in bone from adults, indicating that bone remodelling was restricted to adults.

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Bones and Teeth, Histology of

Lisa N. Cooper , Mary C. Maas , in Encyclopedia of Marine Mammals (Tertiary Edition), 2018

A Bone Structure and Composition

Bone consists of a highly calcified, extracellular bone matrix, and cells ( Fig. ane). Bone matrix (also known as osteoid) consists of well-nigh 33% organic thing (mostly Type I collagen) and 67% inorganic thing (calcium phosphate, mostly hydroxyapatite crystals). Bone is commonly classified co-ordinate to its gross appearance every bit cancellous bone (bone with numerous, macroscopic interconnecting cavities, or trabeculae, likewise known every bit spongy or trabecular bone) or meaty bone (dense lamellar bone without trabeculae), simply both types have the same basic histological structure. In a typical mammalian long bone, the diaphysis (shaft) is composed predominantly of compact bone, with cancellous bone confined to the inner surface effectually a fundamental medullary cavity while the epiphyses (articular ends) consist mostly of cancellous os overlain past a thin, shine layer of compact bone (Fig. 1A, 2A). In curt bones, a core of cancellous bone is completely surrounded past meaty bone, and in the flat bones of the skull, inner and outer plates of meaty bone are separated by the diploë, a layer of cancellous os.

Effigy 1. (A) Schematic model of the wall of a mammalian long-bone diaphysis, consisting of an outer layer of compact bone and an inner layer of cancellous bone, surrounding a central medullary cavity. Periosteum covers the outer bone surface, and endosteum covers the inner os surface. (B) Enlarged diagram of periosteum and compact bone in (A). 1, osteon; 2, haversian canal; three, interstitial lamellae; 4, outer circumferential lamellae; 5, cancellous bone; half-dozen, Volkman's canal; 7, periosteum; eight, Sharpey'due south fibers; 9, lacuna; x, concentric lamellae.

Adapted from Ten Cate (1989).

Figure two. The long basic of terrestrial mammals have a different organization compared to marine mammals. (A) Most terrestrial mammals take a diaphysis equanimous predominantly of compact os, with cancellous bone residing in the medullary cavity. Marine mammals brandish 2 long bone phenotypes. (B) The long bones of virtually deep-diving and fast-swimming cetaceans are composed almost exclusively with cancellous bone, or osteosclerotic. (C, D) Shallow-swimming marine mammals, like manatees, accept long bones fabricated about entirely of thickened compact bone. X-rays of the humerus of (A) deer, (B) beluga, and (C) manatee. (D) Pachyosteosclerotic humerus of a manatee cutting in half, to reveal the absenteeism of a medullary cavity and the extent cortical os has infiltrated the medullary crenel. Scale bar is ane   cm in length.

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Nutrients and Gene Expression Affecting Os Metabolism

José Luis Pérez-Castrillón , José Antonio Riancho del Moral , in Principles of Nutrigenetics and Nutrigenomics, 2020

Osteocytes

Osteocytes are cells derived from osteoblasts that are embedded in the bone matrix. Between v% and 20% of osteoblasts are transformed into osteocytes. Osteocytes express some genes expressed past osteoblasts and others, such as sclerostin and genes related to bone mineralization and phosphorus metabolism, such as dentin matrix acidic phosphoprotein (DMP) and fibroblast growth factor (FGF)23, which are osteocyte-specific. They are located in lacunae and feature cytoplasmic dendritic processes in the canaliculi within the bone matrix that let intercellular communication. In addition, because they are related to bone cells, they communicate with the claret vessels. These cells behave similar mechanostats, responding to mechanical forces regulating bone germination and resorption. They are the main producers of sclerostin, which is encoded by the sclerostin (SOST) factor. Sclerostin antagonizes various os morphogenetic proteins (BMPs) and binds to depression-density lipoprotein receptor-related 5/half dozen (LPR5/LPR6), blocking the canonical wingless (Wnt) pathway. In addition to inhibiting bone formation, osteocytes may also initiate resorption, either past segregating the receptor activator for nuclear cistron-κB ligand (RANKL) or indirectly after apoptosis, by stimulating the production of RANKL by osteoblasts or cells of the osteoblast lineage. These cells produce osteoprotegerin that competes with RANKL and blocks resorption ( Bonewald and Johnson, 2008).

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